Combining chat-related efforts

Angelo has developed https://github.com/solid-contrib/data-modules/tree/main/chats
There is https://github.com/solid-contrib/gitter-solid which already existed
And I'm now working on https://github.com/tubsproject/solid-slack-bridge which Reza and Yashar built last year for a hackathon.

Apart from that, @jaxoncreed is now working on milestone M5 at the same time, so useful to coordinate!